1. Field of the Invention
This invention relates to a centrifugally activated variable damper assembly. More particularly, this invention relates to a centrifugally activated variable damper assembly to be used preferably in connection with a stopped-rotor aircraft (see, U.S. Pat. No. 5,454,530) to provide smooth transition during the conversion process from rotary wing to fixed-wing flight, or vise versa. With greatest particularity, the invention relates to a centrifugally activated variable damper and associated linkages to adjust the damping level of the rotor blades and hub about the teetering connection to the mast to be produced depending upon the flight configuration.
2. Background Information
Various types of aerial vehicles have been proposed which would be capable of vertical takeoff and landing as well as flying like a fixed-wing aircraft, such as the stowed-rotor and X-wing. These concepts may be different in design, yet attempt to achieve similar operational goals of vertical takeoff and landing, and high-speed forward flight.
The concept known as the stowed-rotor behaves like a conventional helicopter for vertical takeoff and landing. For high speed forward flight the rotors are stopped and stowed out of the way of the air stream to reduce drag, while a set of conventional fixed-wing airfoils assume primary lift. U.S. Pat. No. 4,127,244 to Pender (1978) show the complexity involved in stopping and folding the rotors. Similar aircraft require the additional weight of a fixed-wing, as well as the complexity and aerodynamic drag of a stowed-rotor.
Other concepts of the aforesaid aircraft such as the X-wing use a rotor for vertical and translational flight. In the helicopter mode, the rotors rotate to provide for verticals take off and landing. For flight in the fixed-wing mode, the rotor is eventually stopped and locked to the body of the aircraft.
The complexity and number of mechanisms associated with a main rotor structure used in helicopter mode flight, and the differing stiffness requirements of the rotor relative to the mast of the aircraft in helicopter and fixed-wing flight mode, greatly complicates the challenge of successfully transitioning between rotary-wing and fixed-wing flight, and vise versa.
For the purpose of this disclosure, further discussion will be based on a two-bladed teetering rotor with a rigid hub between the two blades. Accordingly, in order to provide acceptable dynamic loads and gust sensitivity while in helicopter mode, the rotor blades and hub need to be free to teeter about the connection to the mast with relatively low stiffness. Yet to attain high speed flight while in fixed-wing mode, the hub-to-mast stiffness must be orders of magnitude higher in fixed-wing mode than the low stiffness required for helicopter mode. Furthermore, during the conversion process from helicopter mode to fixed-wing mode, the blades and hub may have a tendency to teeter due to high forward velocity of the aircraft and gusts encountered during flight. A sudden increase in stiffness while the rotor is teetering causes high loads in the rotor system due to the abrupt stopping of the teetering motion.
It is seen then that it would be desirable to have a variable damper assembly in the rotor system of a stopped-rotor aircraft to adjust the damping level to be produced depending upon the flight configuration of the aircraft as the aircraft transitions from rotary-wing to fixed-wing flight, or vise versa. The present invention incorporates a centrifugally activated damper assembly for use in a stopped-rotor aircraft to dampen the teetering motions of the rotor blades depending upon the centrifugal forces acting upon the assembly produced by the rotation of the rotor system as a function of the aircraft flight configuration.